1. Field of the Invention (Technical Field)
The present invention relates to the use of directed laser energy to ablate materials from surfaces, particularly for the removal of contaminants and buildups from industrial components, especially methods and apparatus for laser ablation cleaning of commercial electrical generators.
2. Background Art
Laser ablation is not new. But all traditional ablation theories are based on a thermal-process model, delivering enough energy fast enough to take a scud coating directly to a vapor state. In the present invention, resonant energy is coupled directly into bond vibrational frequencies. For example, hydrocarbon molecules that make up linseed oil are literally torn apart by quickly forcing the vibrations between atoms making up the molecules, such as Cxe2x80x94C, Cxe2x95x90C, Cxe2x80x94O, and Cxe2x80x94H, to vibrate so violently that the bonds break. This is different from thermal-process models for laser ablation.
There commonly are many kinds of coatings such as paint, grease, oils, plasma-vapor-deposited metal, and the like on various surfaces such as metals, concrete, wood, laminates, plastics, etc. The surface is referred to as the xe2x80x9csubstratexe2x80x9d and the coating is referred to as the xe2x80x9ccoating.xe2x80x9d A given kind of substrate may have several different kinds/layers of coatings. A frequent need in various industries is the removal of a coating without damaging the substrate. This need arises when cleaning or rehabilitating industrial machines, equipment and structures, for instance.
There are various known ways to remove coatings. Nearly all current coating removal technologies exhibit one or more of three shortcomings: (1) they can cause damage to the substrate, (2) they do not clean out surface pores, or (3) they result in a volume of waste that is larger than the volume of removed coating material (e.g., it takes about 100 pounds of sand to remove 1 pound of aged lead-based paint by sand-blasting). Further, many existing designs inject or suck air in parallel to, and from one side, of the surface being cleaned, and then evacuate it from the other side; such designs tend to leave residue (xe2x80x9csootingxe2x80x9d) on the target surface due to asymmetric flow.
The following references are also of interest by way of background: xe2x80x9cKeeping Reactions Under Quantum Control,xe2x80x9d by S. Hurley and A. Castleman, Science, v. 292, p. 648, 27 (April 2001); xe2x80x9cSelective Bond Dissociation and Rearrangement with Optimally Tailored, Strong-Field Laser Pulses,xe2x80x9d by R. Lewis, G. Menkir, and H. Rabitz, Science, v.292, p. 709, 27 (April 2001); U.S. Pat. No. 6,163,636, xe2x80x9cOptical Communication System Using Multiple-order Raman Amplifiersxe2x80x9d.
Laser ablation cleaning apparatus. An optical box containing mirrors for specially directing laser light, such as repeated pulsed CO2 laser, is mounted in a hand-held cleaning head or in a custom work head. The hand-held cleaning head can be used to safely direct laser energy to a surface to be cleaned; the laser beam ablates from the surface coatings, corrosion, and the like without harming the substrate. The custom work head is removably mountable upon the iron core stack of a conventional commercial electric generator, and features an optics box carriage that is selectively movable along the axis of the stack to direct a laser beam into the slots of the stack for cleaning.
Thus, according to the apparatus system of the invention, there is provided two types of working heads, a portable hand-held cleaning head, and a larger custom work head specially adapted for cleaning the slots in the core stacks of commercial electric generators during generator rehabilitation.
There is disclosed an apparatus for performing laser ablation cleaning of a surface, the apparatus comprising: a laser source for generating a laser beam; a beam delivery system for transmitting the beam from the source to a workhead; and a workhead, the workhead comprising: (1) an optical box having a beam entrance and a beam exit and enclosing an interior containing a first mirror and a second mirror for directing the beam from the entrance toward the surface; (2) means for positively pressurizing the interior of the optical box to induce an air stream out the beam exit; and (3) a vacuum nozzle adjacent the beam exit, the nozzle in fluid communication with a vacuum unit for providing negative pressure in the nozzle to induce an airflow through the nozzle; wherein material ablated from the surface is entrained into the airflow in the nozzle. The laser source preferably is a pulse repetition laser, and the laser beam is broad upon entrance into the optical box and the second mirror focuses the beam, whereby the energy density of the beam is increased by passage through the optical box. A baffle preferably is disposed at the exit to minimize the entry of ablated material into the optical box while permitting the transmission of the beam from the exit.
When the workhead is a hand-held cleaning head, it comprises a triggered gun housing for containing the optical box. When a custom work head is used and the surface to be cleaned is a slot in a core stack of an electrical generator, the stack having a longitudinal axis, the apparatus further comprises: an axial launch mirror for directing the laser beam from the laser source down the longitudinal axis of the core of the stack; at least one adjustable jig assembly, releasably attachable to the core iron stack, for fixing the launch mirror upon the longitudinal axis; at least one carriage rail disposable axially within the core of the stack; means for rotatably mounting the rail to the jig assembly; and a carriage, mounting the workhead including the optical box and nozzle, the carriage movable along the at least one rail for selective axial positioning of the carriage on the longitudinal axis within the core; wherein the carriage is controllably rotatable in relation to the longitudinal axis to radially the beam exit with the slot thereby to direct the laser beam toward the slot. The jig assembly preferably comprises a central hub and at least two spokes extending radially from the hub, the spokes having adjustable lengths, and the spokes of the jig assembly preferably number three uniformly spaced spokes. The jig preferably further comprises means for uniformly adjusting the lengths of the three spokes, thereby to position the axial launch mirror and the carriage on the longitudinal axis of stacks of differing diameters. The second mirror in the optics box ideally is dithered for controlled to-and-fro pivoting to clean the sides, as well as the bottom, of each slot.
The scope of applicability of the present invention will be set forth in part in the detailed description to follow, taken in conjunction with the accompanying drawings, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.